After the barley has been dried, it is ground in a mill into a coarse flour known as grist. This is the raw material for the second stage in the whisky-making process – brewing – which consists of two sequential steps.

The first step is that of mashing:

In this step, the grist is mixed with hot water and stirred in a large container called a mash tun. This process causes the soluble sugars (remember them from Part 1?!) to dissolve, and this sugary liquid (known by the cool name of wort) is drawn off through the perforated floor of the mash tun.

This collection of wort is performed three times, with the temperature of the water used increasing each time from about 60°C in the initial run to approximately 95°C in the third run. While the wort from the first two runs is used as is, the third lot of liquid is used as the first water for the next batch of grist. Waste not, want not. It’s the ultimate in recycling.

The residue of the mashing process (the soggy grist minus its sugar) is referred to as draff, and it gets used to feed cattle. Cows in Scotland, particularly those living close to distilleries, are very well-fed!

The second step in the brewing process is fermentation:

In this step, the wort is cooled to about 20°C, and then fed into more large containers called washbacks. These vessels are traditionally made from wood, although some distilleries now use stainless steel. Easier to clean, but far less character. When you see washbacks during a distillery tour, remember that you are standing on a working floor that has been set about a metre from the top of the containers for easy access. The washbacks continue below the floor and are often about five or six metres tall in total!

It is in these washbacks that fermentation takes place, by adding yeast to the wort. The yeast, a living organism called Saccharomyces Cerevisiae (try saying that after a few drams!), feeds on the sugary liquid and converts this into alcohol.

The washbacks are never completely filled as the fermentation process results in a great deal of frothing, a reaction caused by the release of carbon dioxide as alcohol is produced. Each washback is fitted with revolving blades that cut the head of the froth to prevent overflowing. If you do a distillery tour, the guides will usually let you peep into the washbacks. Remember to take a deep breath (and hold it) before you peer over the edge… failure to do so can quite literally take your breath away if you inhale the carbon dioxide! Don’t worry, it’s not fatal, just very amusing for the rest of the tour party!

After two to three days of fermentation, the result is a low strength (about 5% to 8% alcohol by volume) liquid similar to beer. This liquid is called wash.

This is Part 2 of 4 in a series on the whisky production process:
Part 1 – Malting
Part 2 – Brewing
Part 3 – Distillation
Part 4 – Maturation

Want some more funky fundamentals? Click here to return from Brewing to the Whisky Basics page.